In the operation of nuclear reactors, it is customary to remove fuel assemblies after their energy has been depleted down to a predetermined level. Upon removal, this spent nuclear fuel is still highly radioactive and produces considerable heat, requiring that great care be taken in its packaging, transporting, and storing. In order to protect the environment from radiation exposure, spent nuclear fuel is first placed in a transportable canister. One such type of canister that has gained acceptance in the art is the multi-purpose canister (“MPC”). MPCs are hermetically sealed thermally conductive structures that effectuate the dry storage of spent nuclear fuel and are used to transfer and store said spent nuclear fuel.
In a typical nuclear power plant, an open empty canister is first placed in an open transfer cask. The transfer cask and empty canister are then submerged in a pool of water. Spent nuclear fuel is loaded into the canister while the canister and transfer cask remain submerged in the pool of water. Once fully loaded with spent nuclear fuel, a lid is typically placed atop the canister while in the pool. The transfer cask and canister are then removed from the pool of water, the lid of the canister is welded thereon and a lid is installed on the transfer cask. The canister is then properly dewatered and back filled with inert gas. The canister is then hermetically sealed. The transfer cask (which is holding the loaded and hermetically sealed canister) is transported to a location where a storage cask is located. The canister is then transferred from the transfer cask to the storage cask for long term storage. During transfer from the transfer cask to the storage cask, it is imperative that the loaded canister is not exposed to the environment. Once the storage casks are loaded with the canisters, the canisters must be ventilated so that the heat emanating from the spent nuclear fuel (and thermally conducted through the canister) can be removed from the system.
Spent nuclear fuel that is discharged from light water reactors is stored in the fuel pools so that its decay heat can be removed by tubular heat exchangers known as spent fuel pool coolers. The spent fuel pool coolers, either directly or through an intermediate heat exchanger, reject the waste heat to the plant's ultimate heat sink (such as a river, lake, or sea). The rate of decay heat generation from spent nuclear fuel drops rapidly with the passage of time. Most of the thermal energy produced by the used fuel thus winds up as waste heat rejected to the environment (most of it to the local natural source of water). Only after the heat emission rate has attenuated sufficiently can the fuel be transferred to dry storage. The nuclear plant operators have had little choice in the matter because the available dry storage technologies have strict limits on the decay heat that a loaded canister in dry storage can have. The present day limit on NRC licensed systems is roughly in the range of 20 to 45 kW per canister. The canister, upon transfer to dry storage, continues to reject heat to the environment (now, ambient air, in lieu of a body of water when kept in wet storage).
While attempts have been made to create systems for reclaiming the energy resulting from the heat emanating from nuclear waste at storage sites, such systems are inadequate and/or unrealistic in their implementation. See, for example: (1) U.S. Pat. Nos. 3,911,684; 4,292,536; 5,771,265; and U.S. Patent Application Publication No. 2010/0199667. These systems are not particularly suited to work with canister-based dry storage and/or can not be realistically implemented on-site at nuclear power plants. Thus, a need exists for a system and method for reclaiming the energy potential from the heat emanating from nuclear waste that takes the aforementioned deficiencies into consideration.